U.S. patent number 8,517,095 [Application Number 12/852,915] was granted by the patent office on 2013-08-27 for method of using hexose oxidases to create hydrogen peroxide in aqueous well treatment fluids.
This patent grant is currently assigned to Baker Hughes Incorporated. The grantee listed for this patent is Charles David Armstrong, Qi Qu. Invention is credited to Charles David Armstrong, Qi Qu.
United States Patent |
8,517,095 |
Armstrong , et al. |
August 27, 2013 |
Method of using hexose oxidases to create hydrogen peroxide in
aqueous well treatment fluids
Abstract
A hydrocarbon-bearing subterranean formation may be treated with
an aqueous well treatment fluid which contains a hexose oxidase,
such as glucose oxidase, mannose oxidase or galactose oxidase. The
aqueous well treatment fluid further may contain a viscosifying
polymer and an aldohexose. The aldohexose reacts in-situ with the
hexose oxidase and molecular oxygen to produce hydrogen peroxide.
The hydrogen peroxide may then act as a breaker.
Inventors: |
Armstrong; Charles David
(Tomball, TX), Qu; Qi (Spring, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
Armstrong; Charles David
Qu; Qi |
Tomball
Spring |
TX
TX |
US
US |
|
|
Assignee: |
Baker Hughes Incorporated
(Houston, TX)
|
Family
ID: |
44629611 |
Appl.
No.: |
12/852,915 |
Filed: |
August 9, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20120031618 A1 |
Feb 9, 2012 |
|
Current U.S.
Class: |
166/252.5;
166/305.1; 166/300 |
Current CPC
Class: |
C09K
8/685 (20130101); C09K 8/90 (20130101); C09K
8/52 (20130101); E21B 43/16 (20130101); C09K
8/58 (20130101); C09K 8/887 (20130101); C09K
2208/24 (20130101); C09K 2208/28 (20130101) |
Current International
Class: |
E21B
47/00 (20060101); E21B 43/27 (20060101) |
Field of
Search: |
;166/305.1,252.5,300 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Silverman, The Organic Chemistry of Enzyme-Catalyzed Reactions,
2000, pp. 121-123, Academic Press, San Diego, California. cited by
applicant .
SIGMA, Glucose Oxidase Type VII from Aspergillus Niger, Product
Information Sheet, Sigma, Saint Louis, Missouri. cited by applicant
.
SIGMA, Glucose (GO) Assay Kit, Product Information Sheet, Technical
Bulletin, Sigma, Saint Louis, Missouri. cited by applicant .
C.D. Armstrong, et al., The Next Generation of Regenerative
Catalytic Breakers for Use in Alkaline and High-Temperature
Fracturing Fluids; SPE 127936 (2010). cited by applicant.
|
Primary Examiner: DiTrani; Angela M
Assistant Examiner: Loikith; Catherine
Attorney, Agent or Firm: Jones; John Wilson Jones &
Smith, LLP
Claims
What is claimed is:
1. A method of treating a subterranean formation penetrated by a
wellbore which comprises: (a) introducing into the wellbore an
aqueous well treatment fluid comprising a polysaccharide
viscosifying agent and a hexose oxidase and increasing the
viscosity of the well treatment fluid in-situ; (b) producing
hydrogen peroxide in-situ by activating the hexose oxidase with an
aldohexose to produce a lactone and then reacting the lactone with
oxygen, in the presence of the activated hexose oxidase; (c)
reducing the viscosity of the well treatment fluid by reacting the
hydrogen peroxide with the viscosifying agent.
2. The method of claim 1, wherein the aldohexose of claim (b) is
generated in-situ.
3. The method of claim 2, wherein the aldohexose is produced
in-situ by reacting the polysaccharide viscosifying agent with an
enzyme or hydrogen peroxide.
4. The method of claim 1, wherein the aqueous well treatment fluid
introduced into the wellbore further contains an aldohexose.
5. The method of claim 1, wherein the aldohexose is selected from
the group consisting of allose, altrose, glucose, mannose, gulose,
idose, galactose and talose.
6. The method of claim 5, wherein the aldohexose is selected from
the group consisting of glucose, mannose and galactose.
7. The method of claim 1, wherein the hexose oxidase is selected
from the group consisting of glucose oxidase, mannose oxidase and
galactose oxidase.
8. The method of claim 7, wherein the hexose oxidase is glucose
oxidase.
9. The method of claim 1, wherein the polysaccharide viscosifying
agent is selected from the group consisting of cellulosic
derivatives, galactomannan or a galactomannan derivative, xanthan,
succinoglycan and scleroglucan.
10. The method of claim 9, wherein the polysaccharide viscosifying
agent is a cellulosic derivative selected from the group consisting
of hydroxyalkyl celluloses, alkylcarboxyhydroxy celluloses and
carboxyalkyl cellulose derivatives.
11. The method of claim 10, wherein the cellulosic derivative is
selected from the group consisting of hydroxyethyl cellulose,
methylhydroxyethyl cellulose, ethylhydroxyethyl cellulose,
carboxymethylhydroxyethyl cellulose and methylhydroxypropyl
cellulose.
12. The method of claim 9, wherein the polysaccharide viscosifying
agent is selected from the group consisting of guar gum,
hydroxypropylguar, carboxymethylguar,
carboxymethylhydroxypropylguar, xanthan gum and scleroglucan.
13. The method of claim 9, wherein the galactomannan or
galactomannan derivative is guar or a guar derivative.
14. The method of claim 1, wherein the molar ratio of
aldohexose:hexose oxidase in step (b) is between from about 1:10 to
about 10:1.
15. The method of claim 1, wherein the molar ratio between the
aldohexose, oxygen and hexose oxidase in step (b) is 1:1:1.
16. The method of claim 1, wherein the pH of the well treatment
fluid introduced into the wellbore is between from about 5.5 to
about 10.5.
17. The method of claim 1, wherein the well treatment fluid
introduced into the wellbore further comprises a crosslinking
agent.
18. The method of claim 1 wherein the well treatment fluid is a
fracturing fluid.
19. A method of treating a subterranean formation penetrated by a
wellbore which comprises: (a) introducing into the wellbore an
aqueous well treatment fluid having a pH between from about 5.5 to
about 10.5, the aqueous well treatment fluid comprising a
polysaccharide viscosifying agent, a crosslinking agent, an
aldohexose and a hexose oxidase; (b) oxidizing the aldohexose with
oxygen in the presence of the hexose oxidase to produce a lactone
and reducing the hexose oxidase; (c) reacting the reduced hexose
oxidase with oxygen to generate hydrogen peroxide; (d) lowering the
pH of the well treatment fluid with the carboxylated derivative of
the aldohexose hydrolyzed from the lactone; and (e) degrading the
polysaccharide viscosifying agent by reacting the hydrogen peroxide
generated in step (b) with the polysaccharide viscosifying
agent.
20. The method of claim 19, wherein the molar ratio of
aldohexose:hexose oxidase in the aqueous well treatment fluid is
between from about 1:10 to about 10:1.
21. The method of claim 19, wherein the molar ratio of the
aldohexose:oxygen:hexose oxidase in step (b) is 1:1:1.
22. The method of claim 19, wherein the polysaccharide viscosifying
agent is a polysaccharide selected from the group consisting of
guar and guar derivatives.
23. A method of treating a subterranean formation penetrated by a
wellbore which comprises: (a) introducing into the wellbore an
aqueous well treatment fluid comprising a polysaccharide, a
crosslinking agent capable of hydrogen bonding with the
polysaccharide, a hexose oxidase and an aldohexose, the viscosity
of the well treatment fluid increasing after introduction of the
aqueous well treatment fluid into the wellbore; (b) hydrolyzing the
polysaccharide to form a monosaccharide; (c) activating the hexose
oxidase with the aldohexose to form a reduced form of the hexose
oxidase while further forming, from the monosaccharide, a lactone;
(d) reacting the lactone with oxygen in the presence of the reduced
form of the hexose oxidase and water to generate hydrogen peroxide
and a carboxylic acid while restoring the hexose oxidase to its
initial oxidized state; (e) degrading the polysaccharide with the
hydrogen peroxide produced in step (d); (f) reducing the efficacy
of the crosslinking agent to hydrogen bonding to the polymer by
reducing the pH of the fracturing fluid with the generated
carboxylic acid of step (d) thereby lowering the viscosity of the
well treatment fluid.
24. The method of claim 23, wherein the pH of the aqueous well
treatment fluid introduced into the wellbore in step (a) is between
from about 5.5 to about 10.5.
25. The method of claim 23, wherein the polysaccharide is guar or a
guar derivative.
26. The method of claim 23, wherein the aldohexose is selected from
the group consisting of allose, altrose, glucose, mannose, gulose,
idose, galactose and talose.
27. The method of claim 26, wherein the aldohexose is selected from
the group consisting of glucose, mannose and galactose.
28. The method of claim 23, wherein the hexose oxidase is selected
from the group consisting of glucose oxidase, mannose oxidase and
galactose oxidase.
29. The method of claim 28, wherein the hexose oxidase is glucose
oxidase.
30. A method of treating a subterranean formation penetrated by a
wellbore which comprises: (a) introducing into the wellbore an
aqueous viscous well treatment fluid comprising guar or a guar
derivative; a crosslinking agent, a hexose oxidase and an
aldohexose seed, wherein guar or guar derivative hydrolyzes to a
monosaccharide after being introduced into the wellbore; (b)
activating the hexose oxidase with the aldohexose seed and
producing a lactone from the monosaccharide; (c) reacting the
lactone with oxygen in the presence of the activated hexose oxidase
to generate hydrogen peroxide; and (d) degrading the guar or guar
derivative with the hydrogen peroxide.
31. The method of claim 30, wherein the aqueous viscous well
treatment fluid introduced into the wellbore is a fracturing
fluid.
32. A method of slickwater fracturing a subterranean formation
penetrated by a wellbore comprising: (a) introducing into the
wellbore an aqueous well treatment fluid void of a viscosifying
polymer, wherein the well treatment fluid comprises a polymeric
friction reducing agent, a hexose oxidase and an aldohexose; (b)
producing hydrogen peroxide in-situ by reacting an aldohexose and
oxygen, in the presence of the hexose oxidase, (c) reducing the
viscosity of the well treatment fluid by reacting the hydrogen
peroxide with the polymeric friction reducing agent.
33. A method of treating a subterranean formation penetrated by a
wellbore which comprises: (a) forming a filter cake within the
wellbore containing a polysaccharide viscosifying agent; (b)
introducing into the wellbore a well treatment fluid comprising
hexose oxidase; (c) activating the hexose oxidase with aldohexose;
(d) hydrolyzing the polysaccharide viscosifying agent to a
monosaccharide and producing a lactone from the monosaccharide; (e)
reacting the lactone with oxygen in the presence of the activated
hexose oxidase to generate hydrogen peroxide; and (f) degrading the
polysaccharide in the filter cake with the hydrogen peroxide.
34. The method of claim 33, wherein the monosaccharide formed in
step (d) is selected from the group consisting of allose, altrose,
glucose, mannose, gulose, idose, galactose and talose.
35. The method of claim 33, wherein the hexose oxidase is selected
from the group consisting of glucose oxidase, mannose oxidase and
galactose oxidase.
36. The method of claim 35, wherein the hexose oxidase is glucose
oxidase.
37. The method of claim 33, wherein the aldohexose is a component
of the treatment fluid or is generated in-situ.
38. A method of increasing the flow of production fluids from a
subterranean formation penetrated by a wellbore by removing a
filter cake within the subterranean formation, the method
comprising: (a) activating hexose oxidase in-situ with an
aldohexose; (b) hydrolyzing polysaccharide within the filter cake
to a monosaccharide and producing a lactone from the
monosaccharide; (c) reacting the lactone with oxygen in the
presence of the activated hexose oxidase to generate hydrogen
peroxide; and (d) degrading the polysaccharide in the filter cake
with the hydrogen peroxide.
39. The method of claim 38, wherein the aldohexose is selected from
the group consisting of allose, altrose, glucose, mannose, gulose,
idose, galactose and talose.
Description
FIELD OF THE INVENTION
Hexose oxidases are used for the in-situ creation of hydrogen
peroxide, as breaker, for well treatment fluids. The breaker is
produced in the presence of an aldohexose, such as glucose,
galactose or mannose. The aldohexose is either a component of the
well treatment fluid or is generated in-situ.
BACKGROUND OF THE INVENTION
Hydraulic fracturing is used to create subterranean fractures that
extend from the borehole into the rock in order to increase the
rate at which fluids can be produced from the formation. Generally,
a fracturing fluid is pumped into the well at high pressure. Once
natural reservoir pressures are exceeded, the fracturing fluid
initiates a fracture in the formation which continues to grow
during pumping. The treatment design generally requires the fluid
to reach maximum viscosity as it enters the fracture.
The fracturing fluid typically contains a proppant which is placed
within the produced fracture. The proppant remains in the produced
fracture to prevent the complete closure of the fracture and to
form a conductive channel extending from the wellbore into the
treated formation.
Most fracturing fluids contain a viscosifying agent in order to
increase the capability of proppant transport into the fracture.
Suitable viscosifying agents include synthetic polymers, like
polyvinyl alcohols, polyacrylates, polypyrrolidones and
polyacrylamides, and polysaccharides, like guar gum
(galactomannans) and guar gum derivatives. Exemplary guar or guar
gum derivatives include hydroxypropyl guar (HPG), carboxymethyl
guar (CMG) and carboxymethylhydroxypropyl guar (CMHPG) as well as
high molecular weight non-derivatized guar.
Once the high viscosity fracturing fluid has carried the proppant
into the formation, breakers are used to reduce the fluid's
viscosity. In addition to facilitating settling of the proppant in
the fracture, the breaker also facilitates fluid flowback to the
well. Breakers work by reducing the molecular weight of the
viscosifying agent. The fracture then becomes a high permeability
conduit for fluids and gas to be produced back to the well.
Common breakers for use in fracturing fluids include chemical
oxidizers, such as hydrogen peroxide and persulfates. Chemical
oxidizers produce a radical which then degrades the viscosifying
agent. This reaction is limited by the fact that oxidizers work in
a stoichiometric fashion such that the oxidizer is consumed when
one molecule of oxidizer breaks one chemical bond of the
viscosifying agent. Further, at low temperatures, such as below
120.degree. F., chemical oxidizers are generally too slow to be
effective and other catalysts are needed to speed the rate of
reaction. At higher temperatures, chemical oxidizers function very
rapidly and often must be encapsulated in order to slow the rate of
reaction. Alternatives have been sought for maximizing the
efficiency of chemical oxidizers in the well treatment fluid at
in-situ conditions.
More recent interest in hydraulic fracturing has focused on
slickwater fracturing which is often used in the stimulation of
tight gas reservoirs. In slickwater fracturing, a well is
stimulated by pumping water at high rates into the wellbore,
thereby creating a fracture in the productive formation. Slickwater
fluids are basically fresh water or brine having sufficient
friction reducing agent(s) to minimize tubular friction pressures.
Generally, such fluids have viscosities only slightly higher than
unadulterated fresh water or brine. Such fluids are much cheaper
than conventional fracturing fluids which contain a viscosifying
agent. In addition, the characteristic low viscosity of such fluids
facilitates reduced fracture height growth in the reservoir during
stimulation.
When aqueous fluids (like slickwater fracturing fluids) not
containing a viscosifying polymer are used in stimulation, the
pressure during the pumping stage is normally lower than that
required in fracturing treatments using viscosifying polymers. The
frictional drag of the frac fluid is lowered by the presence of the
friction reduction agent(s) in the slickwater fluid. While
slickwater fluids introduce less damage into the formation in light
of the absence of viscosifying polymers, the friction reduction
agent, if left in the formation, can cause formation damage.
Effective means of degrading friction reduction agents in
slickwater fracturing fluids is desired in order to minimize damage
to the treated formation.
SUMMARY OF THE INVENTION
A hydrocarbon-bearing subterranean formation may be treated with an
aqueous well treatment fluid containing a hexose oxidase. Hydrogen
peroxide is generated in-situ by reaction of an aldohexose and
oxygen in the presence of the hexose oxidase. The hydrogen peroxide
may act as chemical breaker in the hydrolysis of a viscosifying
polymer present in the well treatment fluid. Alternatively, the
hydrogen peroxide may function to degrade a friction reduction
agent in a well treatment fluid. Further, the hydrogen peroxide may
function to degrade a polymeric component of a filter cake.
The aldohexose may be a component in the aqueous well treatment
fluid. Alternatively, the aldohexose may be generated in-situ.
The aldohexose seeds the reaction for the generation of a small
amount of hydrogen peroxide. The hydrogen peroxide produced from
the seed reaction breaks at least a portion of the viscosifying
polymer, friction reduction agent or the polymeric component of the
filter cake which then reacts with oxygen, in the presence of the
hexose oxidase, to create greater quantities of hydrogen peroxide.
Thus, as the polysaccharide viscosifying agent or
polysaccharide-based filter cake degrades, more and more breaker is
produced. This then serves to effectuate the complete degradation
of the polysaccharide viscosifying agent or polysaccharide-based
filter cake. As such, the polysaccharide viscosifying agent or
polysaccharide-based filter cake becomes the source of the
breaker.
As an example, hydrogen peroxide produced from the seed reaction of
aldohexose may break a small portion of a polysaccharide
(functioning as viscosifying polymer) in a well treatment fluid
into monosaccharide units. The monosaccharide units then react with
oxygen, in the presence of the hexose oxidase, to create greater
quantities of hydrogen peroxide. Degradation of the polysaccharide
produces greater quantities of breaker which effectuates the
complete degradation of the polysaccharide.
Exemplary of the invention is an aqueous well treatment fluid
containing guar, beta D-glucose and glucose oxidase, a
flavin-dependent enzyme. Reaction of the glucose with oxygen in the
presence of the enzyme produces hydrogen peroxide and
D-glucono-1,5-lactone. Other beta-D-monosaccharides, such as
galactose and mannose, may also be converted to lactones by glucose
oxidase. As hydrogen peroxide is produced, it attacks the guar and
degrades guar to produce smaller molecular weight fragments
including the monosaccharides galactose and mannose. The enzyme can
then use these liberated monosaccharides to produce more hydrogen
peroxide which further degrades the guar polymer.
In addition to the embodiment wherein the well treatment fluid is a
fracturing fluid containing a viscosifying agent, the well
treatment fluid may further be a fracturing fluid containing a
polymeric friction reducer for use in slickwater fracturing. When
used as a slickwater fracturing fluid, the hydrogen peroxide breaks
the polymeric friction reducer. In the manner described above, the
hydrogen peroxide is generated in situ by reaction of an aldohexose
and oxygen in the presence of an aldohexose.
In addition, the well treatment fluid may be used to clean up a
fluid loss pill, typically used during completion of the well. In
such an instance, the well treatment fluid aids in the removal of
the filter cake formed by the fluid loss pill. In addition, the
well treatment fluid may be used to remove the filter cake from
drilling fluid or drill-in fluid formed during drilling.
BRIEF DESCRIPTION OF THE DRAWINGS
In order to more fully understand the drawings referred to in the
detailed description of the present invention, a brief description
of each drawing is presented, in which:
The FIGURE demonstrates the reduction in viscosity of an aqueous
fluid containing a crosslinked polysaccharide by the action of
glucose oxidase when seeded with a hexoaldose.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The method disclosed herein consists of treating a
hydrocarbon-bearing subterranean formation penetrated by a wellbore
with an aqueous well treatment fluid which contains a hexose
oxidase. The hexose oxidase in the aqueous well treatment fluid of
the invention is preferably glucose oxidase, mannose oxidase or
galactose oxidase. Typically, the amount of hexose oxidase in the
aqueous well treatment fluid is typically between from about
1.0.times.10.sup.-3 to about 1.0 percent by volume.
The aqueous well treatment fluid may further contain a viscosifying
agent. The viscosifying agent serves to increase the viscosity of
the aqueous well treatment fluid and is hydrolyzed by the
enzymatically produced hydrogen peroxide. When present, the amount
of viscosifying agent in the aqueous well treatment fluid is
between from about 0.10% to 5.0% by weight of the aqueous fluid.
The most preferred range for the present invention is about 0.20%
to 0.80% by weight.
Preferred viscosifying agents include polysaccharides which may be
hydrolyzed by the enzymatically produced hydrogen peroxide to form
monosaccharide units and other low molecular weight fragments.
Suitable polysaccharides may be ionic as well as nonionic.
Preferred are cellulose, starch, and galactomannan gums, such as
non-derivatized and derivatized guar. The polysaccharide may be a
microbial polysaccharide such as xanthan, succinoglycan and
scleroglucan.
Suitable cellulose and cellulose derivatives include
alkylcellulose, hydroxyalkyl cellulose or alkylhydroxyalkyl
cellulose, carboxyalkyl cellulose derivatives such as methyl
cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose,
hydroxybutyl cellulose, hydroxyethylmethyl cellulose,
hydroxypropylmethyl cellulose, hydroxylbutylmethyl cellulose,
methylhydroxyethyl cellulose, methylhydroxypropyl cellulose,
ethylhydroxyethyl cellulose, carboxyethylcellulose,
carboxymethylcellulose and carboxymethylhydroxyethyl cellulose.
Specific galactomannan gums and derivatized galactomannan gums
include guar gum, hydroxypropyl guar, carboxymethyl guar,
hydroxyethyl guar, hydroxypropyl guar, carboxymethylhydroxyethyl
guar, carboxymethylhydroxypropyl guar and known derivatives of
these gums.
Particularly preferred are "GW4" (guar), "GW21" (HEC), "GW22"
(xanthan gum), "GW24L" (HEC slurry), "GW45" (CMG), "GW27" (guar),
"GW28" (CMHEC), "GW32" (HPG), and "GW38" (CMHPG), all available
from Baker Hughes Incorporated. In addition, slurried counterparts
of these polymers are available from Baker Hughes Incorporated as
"XLFC1" (guar), "XLFC1B" (guar), "XLFC2" (HPG), "XLFC2B" (HPG),
"XLFC3" (CMPHG) "XLFC3B" (CMHPG), "VSP1" (CMG), and "VSP2" (CMG),
respectively.
The viscosifying agent may further be a synthetic polymer such as a
polyvinyl alcohol, polyacrylate, polypyrrolidone or polyacrylamide
or a mixture thereof. In addition, the viscosifying polymer may be
a block or random copolymer containing units selected from vinyl
alcohol, acrylates, including the (meth)acrylates, pyrrolidone,
2-acrylamido-2-methylpropane sulfonate and acrylamide including the
(meth)acrylamides.
The pH of the well treatment fluid introduced into the wellbore is
typically between from about 5.5 to about 10.5 and more typically
is between from about 8.5 to about 10.5.
When the well treatment fluid introduced contains a viscosifying
polymer, the fluid further typically contains a crosslinking agent.
Any crosslinking agent capable of hydrogen bonding with the
viscosifying polymer may be employed.
Suitable crosslinking agents include a borate ion releasing
compound, an organometallic or organic complexed metal ion
comprising at least one transition metal or alkaline earth metal
ion as well as mixtures thereof. When present, the amount of
crosslinking agent employed in the composition is typically between
from about 0.001 percent to about 2 percent, preferably from about
0.005 percent to about 1.5 percent, and, most preferably, from
about 0.01 percent to about 1.0 percent.
Borate ion releasing compounds which can be employed include, for
example, any boron compound which will supply borate ions in the
well treatment fluid, for example, boric acid, alkali metal borates
such as sodium diborate, potassium tetraborate, sodium tetraborate
(borax), pentaborates and the like and alkaline and zinc metal
borates. Such borate ion releasing compounds are disclosed in U.S.
Pat. Nos. 3,058,909 and 3,974,077 herein incorporated by reference.
In addition, such borate ion releasing compounds include boric
oxide (such as selected from H.sub.3BO.sub.3 and B.sub.2O.sub.3)
and polymeric borate compounds. Such borate-releasers typically
require a basic pH (e.g., 7.0 to 12) for crosslinking to occur.
Suitable pH adjustment agents, such as soda ash, potassium
hydroxide, sodium hydroxide and alkaline and alkali carbonates and
bicarbonates, may be used to maintained the desired pH.
Further preferred crosslinking agents are organometallic and
organic complexed metal compounds, which can supply zirconium IV
ions such as, for example, zirconium lactate, zirconium lactate
triethanolamine, zirconium carbonate, zirconium acetylacetonate and
zirconium diisopropylamine lactate; as well as compounds that can
supply titanium IV ions such as, for example, titanium ammonium
lactate, titanium triethanolamine, and titanium acetylacetonate. Zr
(IV) and Ti (IV) may further be added directly as ions or oxy ions
into the composition.
The aqueous well treatment fluid is used principally to enhance the
productivity of the formation. In a preferred embodiment, the well
treatment fluid is used as a stimulation fluid, such as one used in
hydraulic fracturing. The heightened viscosity of the fluid enables
the transport of a proppant into the created fractures. Such
proppants serve to prop open the created fractures such that the
fracture provides larger flow channels through which an increased
quantity of a hydrocarbon may flow. Productive capability of the
well is therefore increased.
In addition to the hexose oxidase, the aqueous well treatment
fluids described herein may further contain one or more
aldohexoses. The aldohexose in the well treatment fluid reacts
in-situ with the hexose oxidase and molecular oxygen (within the
wellbore) to produce hydrogen peroxide and a lactone. When present,
the amount of aldohexose in the aqueous well treatment fluid
introduced into the wellbore is that sufficient to produce, in the
presence of the hexose oxidase, a small amount of hydrogen
peroxide. Typically, the amount of aldohexose in the aqueous well
treatment fluid is no greater than 0.001 volume percent. The
produced hydrogen peroxide may then be used to break down the
viscosifying polymer (for example polysaccharide into
monosaccharide units), friction reduction agent or polymeric
component of a filter cake which in turn then produces additional
hydrogen peroxide. In the case of breaking synthetic polymeric
friction reducers, the amount of aldohexose in the aqueous well
treatment fluid is that sufficient to produce the desired amount of
hydrogen peroxide.
When present in the well treatment fluid, the aldohexose functions
as a monosaccharide "seed" to commence generation of a small amount
of hydrogen peroxide in-situ by it reaction with oxygen, in the
presence of the hexose oxidase. Suitable aldohexoses include
allose, altrose, glucose, mannose, gulose, idose, galactose and
talose.
An exemplary catalytic pathway for glucose oxidase (as hexose
oxidase) in the production of hydrogen peroxide in the presence of
a polysaccharide is set forth below in Schematic (I) wherein the
monosaccharides are represented by the open hexagons, the lactone
is represented by the cross-hatched hexagon, and the produced
carboxylic acid is represented by the filled hexagon:
##STR00001##
As illustrated, hydrogen peroxide produced from the seed reaction
breaks a small portion of the polysaccharide (viscosifying polymer)
into monosaccharide units. Such monosaccharide units then react
with the hexose oxidase and oxygen to create greater quantities of
hydrogen peroxide to defragment the polysaccharide. As such, the
aldohexose in the aqueous well treatment fluid when introduced into
the wellbore serves as a seed to generate a small amount of
hydrogen peroxide; much larger amounts of hydrogen peroxide being
produced in-situ as degradation of the polysaccharide continues in
the formation.
Typically, the molar ratio of aldohexose to hexose oxidase in the
aqueous well treatment fluid introduced into the wellbore to
conduct the seed reaction is between from about 1:10 to about 10:1
and the molar ratio between the aldohexose, oxygen and hexose
oxidase is preferably 1:1:1.
Instead of including the aldohexose in the aqueous well treatment
fluid, the aldohexose may be generated in-situ. For instance, where
the aqueous well treatment fluid introduced into the wellbore
contains a polysaccharide as viscosifying agent, the fluid may
further contain a small amount of a conventional enzyme breaker or
chemical breaker, like peroxide. Such a breaker could defragment a
small amount of polymeric viscosifying agent into monosaccharide
units including aldohexose units. Such in-situ generated
aldohexoses may then react with the hexose oxidase and molecular
oxygen to produce hydrogen peroxide, such as in accordance with
Schematic (I) above.
The generation of hydrogen peroxide in accordance with the method
of the invention is believed to proceed by Schematic (II), wherein
the aldohexose if glucose:
##STR00002## As shown, in the presence of glucose oxidase,
GO.sub.x, and oxygen (within the wellbore and/or formation),
glucose is oxidized to its corresponding lactone which hydrolyzes
to the corresponding carboxylic acid, a carboxylated derivative of
the aldohexose. The reduced form of the glucose oxidase further
reacts with oxygen to restore the glucose oxidase to its initial
(oxidized) state and produce hydrogen peroxide. The hydrogen
peroxide then degrades the viscosifying polymer, friction reduction
agent or polymeric component of a filter cake into smaller building
or molecular units which may then, in turn, react with the hexose
oxidase to produce additional hydrogen peroxide by the procedure
set forth above.
The viscosity of the well treatment fluid is thereby gradually
decreased by the hydrogen peroxide produced in-situ in the
formation from the reaction of the glucose oxidase and aldohexose.
The pH is lowered as the carboxylic acid is generated. In, for
example, a well treatment fluid containing a viscosifying polymer,
the lowering of the pH diminishes the efficacy of the crosslinking
agent to hydrogen bonding to the polysaccharide. The lowering of
the pH decreases the viscosity of the well treatment fluid.
When used as a fracturing fluid, any proppant known in the art may
be used in the well treatment fluid. Suitable proppants include
quartz sand grains, glass and ceramic beads, walnut shell
fragments, aluminum pellets and nylon pellets.
Other suitable proppants include ultra lightweight proppants having
an apparent specific gravity less than or equal to 2.45, preferably
less than or equal to 1.75, most preferably less than or equal to
1.25. Suitable ULW particulates include those set forth in U.S.
Patent Publication No. 20050028979, published on Feb. 10, 2005,
herein incorporated by reference. Included therein are naturally
occurring materials which may be strengthened or hardened by use of
modifying agents to increase the ability of the naturally occurring
material to resist deformation. Specific examples of ULW
particulates include, but are not limited to, ground or crushed
shells of nuts such as walnut, coconut, pecan, almond, ivory nut,
brazil nut, etc.; ground or crushed seed shells (including fruit
pits) of seeds of fruits such as plum, olive, peach, cherry,
apricot, etc.; ground or crushed seed shells of other plants such
as maize (e.g., corn cobs or corn kernels), etc.; processed wood
materials such as those derived from woods such as oak, hickory,
walnut, poplar, mahogany, etc., including such woods that have been
processed by grinding, chipping, or other form of particalization,
processing, etc. Further suitable particulates include porous
ceramics or organic polymeric particulates. The porous particulate
material may be treated with a non-porous penetrating material,
coating layer or glazing layer. For instance, the porous
particulate material may be a treated particulate material, as
defined in U.S. Pat. No. 7,426,961, herein incorporated by
reference, wherein (a) the ASG of the treated porous material is
less than the ASG of the porous particulate material; (b) the
permeability of the treated material is less than the permeability
of the porous particulate material; or (c) the porosity of the
treated material is less than the porosity of the porous
particulate material. Further, the ultra lightweight particulate
may be a well treating aggregate composed of an organic lightweight
material and a weight modifying agent. The ASG of the organic
lightweight material is either greater than or less than the ASG of
the well treating aggregate depending on if the weight modifying
agent is a weighting agent or weight reducing agent, respectively.
Where the weight modifying agent is a weighting agent, the ASG of
the well treating aggregate is at least one and a half times the
ASG of the organic lightweight material, the ASG of the well
treating aggregate preferably being at least about 1.0, preferably
at least about 1.25. Such ULW proppants are disclosed in U.S.
Patent Publication No 2008/0087429 A1, herein incorporated by
reference. Further, the ULW proppant may be a polyamide, such as
those disclosed in US-2007-0209795 A1, herein incorporated by
reference. Further, the ULW proppant may be metallic spheres, such
as those disclosed in U.S. Patent Publication No. 2008/0179057 A1
as well as those deformable particulates set forth in U.S. Pat. No.
7,322,411, both of which are herein incorporated by reference.
Still preferred are synthetic polymers, such as polystyrene beads
crosslinked with divinylbenzene. Such beads include those described
in U.S. Pat. No. 7,494,711, herein incorporated by reference.
The well treatment fluid described herein can also contain other
conventional additives common to the well service industry such as
surfactants, corrosion inhibitors, crosslinking delaying agents and
the like.
In addition to functioning as a stimulation fluid, the aqueous well
treatment fluids described herein may also be used as a well
treatment fluid to clean up a fluid loss pill typically used during
completion operations. In this case, the well treatment fluid aids
in the removal of the filter cake formed by the fluid loss pill.
The filter cake, in some instance, may become embedded in the
formation. The treatment fluid for such purposes does not contain a
viscosifying polymer, such as a polysaccharide. The treatment fluid
contains hexose oxidase which reacts with an aldohexose (either in
the treatment fluid or generated in-situ) to produce hydrogen
peroxide. The hydrogen peroxide is then used to break down the
polymeric component, such as a polysaccharide, in the filter cake
in the manner described above. The well treatment fluid therefore
assists in the removal of the filter cake defragmenting the
polymeric component present in the filter cake.
Similarly, the aqueous well treatment fluids described herein may
also be used as a well treatment fluid to remove the filter cake
from drilling fluid or drill-in fluid formed during drilling
operations. In this case, the well treatment fluid aids in the
removal of the filter cake formed by the drilling fluid or drill-in
fluid being deposited directly against the formation. The filter
cake, in some instance, may become embedded in the formation.
Removal of the filter cake is effectuated by breaking down the
polymeric component of the filter cake in the manner described
above. In particular, the hexose oxidase, in conjunction with the
hexoaldose and oxygen, generates hydrogen peroxide. The peroxide,
in turn, defragments the polymeric component and breaks the filter
cake.
In another preferred embodiment, the well treatment fluid described
herein is a fracturing fluid for slickwater fracturing. The aqueous
well treatment fluid for slickwater fracturing typically does not
contain a viscosifying agent such as a viscosifying polymer.
Instead, the well treatment fluid contains a polymeric friction
reducing agent. The hydrogen peroxide generated in-situ from the
reaction of the aldohexose and oxygen, in the presence of the
hexose oxidase, reduces the molecular weight of the friction
reducing agent. The defragmented components of the friction
reducing agent may then be removed from the wellbore and formation
damage from the friction reducing agent is thereby minimized.
Typically, the friction reducing agent in such applications is a
polyacrylamide and polyacrylates. The amount of friction reducing
agents in such well treatment fluids is generally from about 1 to
about 8 pounds per thousand gallons of water. Such slickwater
fracturing methods are particularly desirous when stimulating shale
formations and tight gas sands, as well as limestone.
The following examples are illustrative of some of the embodiments
of the present invention. Other embodiments within the scope of the
claims herein will be apparent to one skilled in the art from
consideration of the description set forth herein. It is intended
that the specification, together with the examples, be considered
exemplary only, with the scope and spirit of the invention being
indicated by the claims which follow.
EXAMPLES
Example 1. A 100 mL aqueous fluid was prepared containing 25 ppt of
a non-derivatized guar having an intrinsic viscosity of
approximately 16.1 dL/g (commercially available as GW3 from Baker
Hughes Incorporated), 1.5 gpt of buffer (commercially available as
BF-7L from Baker Hughes Incorporated), 1.5 gpt of a borate
crosslinking agent (commercially available as XLW-32 from Baker
Hughes Incorporated) and about 25 ug/mL of glucose oxidase,
GO.sub.x. Dextrose was then added at a concentration of
approximately 3 .mu.M. The resulting fluid was then transferred to
a Chandler 5500 viscometer having an R1B1 bob and cup assembly. The
viscosity was then measured at 300 rpm (511 sec.sup.-1) at
140.degree. F. The FIGURE demonstrates the reduction in viscosity
of the crosslinked guar polymer by the action of glucose oxidase.
As shown in the FIGURE, glucose oxidase reduces the viscosity of
the 25 ppt crosslinked guar polymer when seeded with the 3 mM
dextrose. Liberated mannose and galactose monosaccharides are used
by the enzyme to produce hydrogen peroxide and further degrade the
crosslinked guar polymer. In the absence of dextrose, the FIGURE
shows that glucose oxidase does not initiate the reaction and the
crosslinked guar polymer is not broken. The FIGURE also
demonstrates that there is no significant rebounding of the
viscosity of the broken guar polymer as compared to the control
once the samples are cooled to room temperature.
Example 2
Approximately 5.5 mM of mannose, galactose and glucose were
dissolved in three separate vessels containing distilled water and
about 25 ug/mL of glucose oxidase. The concentration of hydrogen
peroxide was then measured by test strips after 5 minutes and 1
hour and the pH of the fluid after one hour was also determined.
The results are set forth in Table I below:
TABLE-US-00001 TABLE I Sugar [H.sub.2O.sub.2].sup.A, mg/L
[H.sub.2O.sub.2].sup.B, mg/L pH.sup.B Mannose 3 10 4.5 Galactose 0
3 5.7 Glucose 10 30 3.7 .sup.A5 minute reaction time. .sup.B1 hour
reaction time.
As shown in Table I, mannose and galactose as well as glucose are
suitable substrates for glucose oxidase. Based on the concentration
of hydrogen peroxide with respect to time, the enzyme's substrate
specificity is glucose>mannose>galactose. This is also
reflected in the pH of the samples after the 5 minute reaction
time. Referring to Sequence II above, the production of a
carboxylic acid from the oxidized lactone provides the recorded
drop in the pH of the fluid. The pH of each of the samples is
consistent with the utilization of the substrate i.e. the more the
reaction progresses, the lower the pH. Additionally, the drop in pH
reduces the efficacy of the crosslinking reaction leading to a
further reduction in the viscosity of the fluid.
From the foregoing, it will be observed that numerous variations
and modifications may be effected without departing from the true
spirit and scope of the novel concepts of the invention.
* * * * *